(1) Field of the Invention
The present invention relates to a system and method for modeling gas generator launchers, and more particularly to a computer-implemented system and method of modeling a device launched by way of a boosted argon hybrid (BAH) energy source.
(2) Description of the Prior Art
When properly designed and implemented, a BAH energy source can be utilized as a device launcher. One such application of a device launcher would be from a submerged vehicle, such as a submarine, which may have a need to launch devices into the surrounding environment. However, since the surrounding environment is at a pressure higher than the interior pressure of a submarine, an elevated pressurized launch system is needed.
One such device launcher is a boosted argon hybrid (BAH) powered gas generator launcher. FIG. 1 shows a typical BAH system with two BAH units 13 and a ram plate 30. During the launch process fuel 22 converts into a hot pressurized gas in the combustion chamber 16, and then flows into a gas expansion tank 18. The pressurized argon then flows through an external orifice 26 into a plenum chamber 24. The gasses expand in the plenum chamber 24, and accelerate the ram plate 30 (if included) and the device being launched 28. Gasses may flow around any gap 25 about the ram plate and device.
One approach to evaluating gas generator launcher designs is to fabricate and actuate test gas generator launchers and to physically measure their performance. As can be appreciated, such fabrication and testing requires construction of the test launcher, fabrication of gas generant fuel and measurement of launcher perimeters, including pressures, temperatures, velocities and acceleration during the actual firing of such a launcher.
This type of testing is labor intensive, time consuming and costly. Physical testing is also expensive because chemical compounds, containers and measuring equipment employed are subject to wear or destruction during each test. In order to test launchers having different dimensions, separate test apparatus must be constructed. Moreover, it would be difficult to vary one or more launcher parameters in order to satisfy the design goals should a specific launcher design fail to satisfy performance goals. Accordingly, parameters that can be modified are limited to fuel composition, geometry and quantity.
Thus, it would be an advancement in the art to provide a system and method of modeling a device launcher which reduces or eliminates the need for fabrication and testing. It is also an advancement to provide such a system and method in a computerized implementation which can be used to predict gas generator performance characteristics without destructive testing of gas generant compounds.
The present invention provides a computer-implemented system and method for evaluating gas generator launchers, which include at least one gas generator having a gas generant fuel housed within a combustion chamber, a tank containing a compressed gas in fluid communication with the combustion chamber through an internal orifice. The internal orifice is sealed with a rupture disk prior to gas generant ignition. The tank is also in fluid communication with a plenum chamber through an external orifice. The external orifice is also sealed with a second rupture disk until the pressure in the compressed gas tank exceeds the design characteristics of the rupture disk. Within the plenum chamber is a device to be launched and, in certain embodiments, a ram plate positioned intermediate the device and the external orifice. The ram plate reduces losses resulting from the blow-by of gasses around the device being launched.
The method includes fixing the system geometry and establishing initial conditions of the launcher to be evaluated. The initial conditions include a mass, composition and geometry of the fuel included in the gas generant, geometries of the tank internal and external orifices and plenum chamber, initial pressures within the pressurized gas tank and plenum chamber, and the mass and geometry of the device to be launched. In addition, if included, the mass of the ram plate must be fixed. Otherwise, the geometry of any gap existing between the device to be launched and the walls of the plenum chamber must be factored into the equation.
Next, a gas generator internal ballistics burn rate is modeled, and an amount of mass and energy added to the combustion chamber as the fuel is consumed is calculated. Then, the rate of mass flux out of the combustion chamber and into the gas tank is modeled utilizing internal orifice geometry, tank and combustion chamber temperatures, tank gas mass, and a ratio of combustion chamber and tank pressure.
A rate of energy flux out of the combustion chamber and into the tank is also modeled using the rate of mass flux out of the combustion chamber and into the tank, the combustion chamber temperature and the specific heat of the combustion chamber gas.
The rate of mass flux and energy flux out of the tank and into the plenum are also modeled utilizing external orifice geometry, tank and plenum temperatures, plenum gas mass and the specific heat of the tank gas. The launch of the vehicle itself is modeled using the mass and energy input into the plenum and subtracting the work imparted upon the vehicle in order to move the vehicle. Finally, losses resulting from blow-by through the gap between the vehicle and the plenum walls, if any, is included in the model.